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Abstract:

Of the many embodiments provided, one embodiment is a drill bit mold
assembly comprising: a mold having a bottom and at least one side; a core
centrally disposed within the mold; and a filter disposed above the
bottom of the mold and within a space formed between the at least one
side of the mold and the core.

Claims:

1. A drill bit mold assembly comprising: a mold cavity having disposed
therein an endpoint of a flow path for molten binder material; and at
least one filter disposed along the flow path before the endpoint of the
flow path.

5. The drill bit mold assembly of claim 1, wherein the filter comprises
at least one of a strainer filter, a cellular filter, a screen filter, a
ceramic cloth filter, a bed filter, a bonded particle filter, a ceramic
foam filter, and any combination thereof.

6. The drill bit mold assembly of claim 1, wherein the mold cavity is
formed by at least one mold assembly piece.

7. The drill bit mold assembly of claim 1, wherein the mold cavity is
formed by at least a mold base operably connected to a funnel.

8. The drill bit mold assembly of claim 1, wherein the mold cavity is
formed by at least a mold base operably connected to a funnel and a gauge
ring.

9. The drill bit mold assembly of claim 1 further comprising: at least
one piece selected from the group consisting of a core, a metal blank, a
leg, a mold insert, and any combination thereof disposed at least
partially within the mold cavity.

10. A drill bit mold assembly comprising: a mold cavity having disposed
therein an endpoint of a flow path for molten binder material; at least a
portion of at least one piece disposed in the mold cavity; at least one
filter disposed along the flow path before the endpoint of the flow path;
and a binder bowl operably attached to the mold cavity and disposed along
the flow path at or before at least one filter.

11. The drill bit mold assembly of claim 10, wherein the piece is
selected from the group consisting of a core, a metal blank, a leg, a
mold insert, and any combination.

14. A method comprising: providing a drill bit mold assembly comprising:
a mold cavity having disposed therein an endpoint of a flow path for a
molten binder material, and at least one filter disposed along the flow
path before the endpoint of the flow path; placing a matrix powder within
the mold cavity; placing a binder material along the flow path before the
filter; melting at least a portion of the binder material to form the
molten binder material; and passing the molten binder material through
the filter so as to infiltrate the matrix powder.

15. The method of claim 14 further comprising: cooling the binder
material to form a drill bit.

16. The method of claim 14 further comprising: removing any filter
material remaining in the drill bit.

17. The method of claim 14, wherein melting involves heating at least a
portion of the binder material to a temperature of about 1100.degree. C.
to about 1230.degree. C.

18. The method of claim 14, wherein passing the molten binder material
through the filter is assisted with pressure.

19. The method of claim 14, wherein the filter comprises a flux.

Description:

[0002] The present invention relates to drill bits and methods of forming
drill bits, and more particularly, to methods and molds for reducing the
amount of inclusions present in drill bits when formed.

[0003] In traditional casting processes, a furnace melts a metal, and the
molten metal is then transferred, typically to another vessel, such as,
for example, a ladle, to transport it to the forming means, such as, a
mold. The furnace can also act as a holding location for the molten metal
to allow any trapped gases and low density impurities to migrate to the
surface. A typical mold used in a casting process may include a number of
components for forming a metallic piece. For example, a common gating
system can comprise a pouring cup connected to a downsprue, which feeds
liquid metals to runners and runner extensions that feed into the final
mold shape. As used herein, "casting" and "casting processes" refer to
this traditional process in which metal is melted at one location and
transferred to a second forming means, such as a mold.

[0004] In the casting of metals, it is generally desirable to separate
exogenous (i.e., originating from sources external to the melt)
intermetallic and non-metallic inclusions from the molten metal. Such
inclusions can result, in molten metals, from impurities included in the
raw materials used to form the melt, from slag, dross and oxides which
form on the surface of the melt as a result of reactions with atmospheric
gases such as oxygen, and from small fragments of the refractory
materials that are used to form the chamber or vessel in which the molten
metal melt is formed. Such inclusions, if not removed from the molten
state of the metal, can result in weakened points in the final formed and
solidified metal body, which is the eventual downstream end product of
the melting operation.

[0005] Typically, in a metal casting process, the molten metal is formed
in a furnace wherein the constituent components are added in the form of
unmelted scrap and/or refined virgin metal, deoxidizing agents in various
forms (both solid and gaseous or a combination of both) and alloying
elements. Very light (less dense) solids and gases tend to migrate to the
surface of the melt where they either effervesce or float in combination
with partially and completely solidified oxides known variously as slag
and dross. Slag can be skimmed off of the molten metal before the molten
metal is removed from the furnace, removing a majority of the impurities
trapped in the slag. Further, a second slag can form in the ladle and be
skimmed off for additional inclusion removal prior to pouring the molten
metal into the casting. The higher density impurities in the melt tend to
remain in some degree of suspension in the liquid phase of the metal, or
melt, as the fluid flow convection currents are generated within that
melt by the heating means applied by the melting furnace. Flux can be
used to chemically bind with some inclusions, allowing them to float or
otherwise be removed from the liquid phase. Those inclusions which are
chemically inert may not be affected by the flux and may therefore remain
suspended in the liquid phase of the metal. In the casting process,
filters have also been used to remove larger inclusions from the molten
metal as it passes into the mold. In such processes, the pressure
provided by the head of the downsprue or some additional pressurization
unit may be used to provide the driving force necessary to pass the
liquid metal through a filter and into the mold.

[0006] For the purposes of this invention, casting should be distinguished
from infiltration (a means of forming a metal object wherein a molten
metal binder is wicked into contact with a powder present in the mold)
processes. Typical casting processes can involve multiple operations that
allow for multiple locations and steps during which inclusions can be
removed. Conversely, operations involving infiltration are more
single-step in orientation, and therefore, do not typically include more
than one step during which the inclusions could be removed. This makes
using a mechanical means to remove inclusions more difficult in
infiltration processes.

SUMMARY OF THE INVENTION

[0007] The present invention relates to drill bits and methods of forming
drill bits, and more particularly, to methods and molds for reducing the
amount of inclusions present in drill bits when formed.

[0008] An embodiment of the present invention comprises a drill bit mold
comprising: a mold having a bottom and at least one side; a core
centrally disposed within the mold; and a filter disposed above the
bottom of the mold and within a space formed between the at least one
side of the mold and the core.

[0009] Another embodiment of the present invention comprises a drill bit
mold comprising: a mold having a bottom and at least one side; a core
centrally disposed within the mold; and a binder bowl disposed on top of
the mold and having a filter incorporated therein.

[0010] Still another embodiment of the present invention comprises a
method comprising: providing a drill bit mold comprising: a funnel; a
mold disposed below the funnel and engaged with the bottom of the funnel;
and a filter disposed above the mold and within the funnel; placing a
matrix powder and a steel blank within the mold; placing a binder
material above the filter; melting at least a portion of the binder
material to form a molten binder material; and allowing the molten binder
material to pass through the filter and infiltrate the matrix powder.

[0011] Yet another embodiment of the present invention comprises an
apparatus comprising: a binder bowl with an opening in a bottom of the
binder bowl; and a filter disposed within the opening in the bottom of
the binder bowl.

[0012] In another embodiment of the present invention, a drill bit mold
assembly may comprise a mold cavity having disposed therein an endpoint
of a flow path for molten binder material; and at least one filter
disposed along the flow path before the endpoint of the flow path.

[0013] In another embodiment of the present invention, a drill bit mold
assembly may comprise a mold cavity having disposed therein an endpoint
of a flow path for molten binder material; at least a portion of at least
one piece disposed in the mold cavity; at least one filter disposed along
the flow path before the endpoint of the flow path; and a binder bowl
operably attached to the mold cavity and disposed along the flow path at
or before at least one filter.

[0014] In another embodiment of the present invention, a drill bit mold
assembly may comprise a mold cavity having disposed therein an endpoint
of a flow path for molten binder material, the mold cavity formed by at
least one inner wall of the drill bit mold assembly and an outer wall of
a piece disposed in the drill bit mold assembly; and at least one filter
disposed along the flow path before the endpoint of the flow path.

[0015] In another embodiment of the present invention, methods may
comprise providing a drill bit mold assembly comprising: a mold cavity
having disposed therein an endpoint of a flow path for a molten binder
material, and at least one filter disposed along the flow path before the
endpoint of the flow path; placing a matrix powder within the mold
cavity; placing a binder material along the flow path before the filter;
melting at least a portion of the binder material to form the molten
binder material; and passing the molten binder material through the
filter so as to infiltrate the matrix powder.

[0016] The features and advantages of the present invention will be
readily apparent to those skilled in the art upon a reading of the
description of the preferred embodiments that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The following figures are included to illustrate certain aspects of
the present invention, and should not be viewed as exclusive embodiments.
The subject matter disclosed is capable of considerable modification,
alteration, and equivalents in form and function, as will occur to those
skilled in the art and having the benefit of this disclosure.

[0018] FIG. 1 is a schematic drawing in section with portions broken away
showing one example of a mold assembly satisfactory for forming a matrix
drill bit in accordance with the teachings of the present disclosure.

[0019] FIG. 2 is a schematic drawing in plan showing interior portions of
one example of a mold satisfactory for use in forming a matrix drill bit
in accordance with the teachings of the present disclosure.

[0020] FIG. 3 is another schematic drawing in section with portions broken
away showing one example of a mold assembly satisfactory for forming a
matrix drill bit in accordance with the teachings of the present
disclosure.

[0021] FIG. 4 is still another schematic drawing in section with portions
broken away showing one example of a mold assembly satisfactory for
forming a matrix drill bit in accordance with the teachings of the
present disclosure.

[0022] FIG. 5 is yet another schematic drawing in section with portions
broken away showing one example of a mold assembly satisfactory for
forming a matrix drill bit in accordance with the teachings of the
present disclosure.

[0023] FIG. 6 is another schematic drawing in section with portions broken
away showing one example of a mold assembly satisfactory for forming a
matrix drill bit in accordance with the teachings of the present
disclosure.

[0024] FIG. 7 is still another schematic drawing in section with portions
broken away showing one example of a mold assembly satisfactory for
forming a matrix drill bit in accordance with the teachings of the
present disclosure.

[0025] FIG. 8 is yet another schematic drawing in section with portions
broken away showing one example of a mold assembly satisfactory for
forming a matrix drill bit in accordance with the teachings of the
present disclosure.

[0026] FIG. 9A is yet another schematic drawing in section with portions
broken away showing one example of a mold assembly satisfactory for
forming a matrix drill bit in accordance with the teachings of the
present disclosure.

[0027] FIG. 9B is a cross-sectional plan view taken along line A-A of FIG.
9A of the layout of one example of a binder bowl satisfactory for use in
forming a matrix drill bit in accordance with the teachings of the
present disclosure.

[0028] FIG. 9C is a cross-sectional plan view taken along line A-A of FIG.
9A of the layout of another example of a binder bowl satisfactory for use
in forming a matrix drill bit in accordance with the teachings of the
present disclosure.

[0029] FIG. 10 is still another schematic drawing in section with portions
broken away showing one example of a mold assembly satisfactory for
forming a matrix drill bit in accordance with the teachings of the
present disclosure.

[0030] FIG. 11 is another schematic drawing in section with portions
broken away showing one example of a mold assembly and an outer mold
assembly satisfactory for forming a matrix drill bit in accordance with
the teachings of the present disclosure.

[0031] FIG. 12 is another schematic drawing in section with portions
broken away showing one example of a mold assembly with a schematic
representation of an external molten binder material source in accordance
with the teachings of the present disclosure.

[0032] FIG. 13 is still another schematic drawing in section with portions
broken away showing one example of a mold assembly satisfactory for
forming a matrix drill bit in accordance with the teachings of the
present disclosure.

[0033] FIG. 14 is a schematic drawing showing an isometric view of a
matrix drill bit having a matrix drill bit body formed in accordance with
the teachings of the present disclosure.

[0034] FIGS. 15A-B are schematic drawings in cross-section and top view
showing a mold assembly satisfactory for forming a test pin in accordance
with the teachings of the present disclosure.

[0035] FIGS. 15C-D are top view pictures showing a mold assembly
satisfactory for forming a test pin in accordance with the teachings of
the present disclosure.

[0036] FIG. 16A is a picture of two test pins formed in accordance with
the teachings of the present disclosure.

[0037] FIG. 16B is a picture of a filter after forming test pins in
accordance with the teachings of the present disclosure.

[0038] FIG. 17 is a scanning electron micrograph of a filter.

[0039] FIG. 18 is a scanning electron micrograph of a filter after forming
a test pin in accordance with the teachings of the present disclosure.

[0040] FIG. 19 is a scanning electron micrograph of a filter after forming
a test pin in accordance with the teachings of the present disclosure.

[0041] FIG. 20 is a scanning electron micrograph of a filter after forming
a test pin in accordance with the teachings of the present disclosure.

[0042] FIG. 21 is a scanning electron micrograph of a filter after forming
a test pin in accordance with the teachings of the present disclosure.

[0043] FIG. 22 is a scanning electron micrograph of a filter after forming
a test pin in accordance with the teachings of the present disclosure.

[0044] FIG. 23 is a scanning electron micrograph of a filter after forming
a test pin in accordance with the teachings of the present disclosure.

DETAILED DESCRIPTION

[0045] The present invention relates to matrix drill bits and methods of
forming matrix drill bits, and more particularly, to methods and molds
for reducing the amount of inclusions present in matrix drill bits when
formed.

[0046] The use of a flux in an infiltration process can help prevent
inclusions from being carried into an infiltrated drill bit. The flux can
bind with oxides such as slag and/or dross, allowing the inclusions to
float and be removed by machining off the top of the bit, commonly
referred to as the "binder head." Carrying out an infiltration process
without flux typically requires the use of a protective atmosphere during
the casting process (e.g., a vacuum or inert) that can be expensive and
require specialized processing equipment. Without intending to be limited
by theory, the inventor has discovered that while the use of flux is
generally considered to be beneficial, the use of a flux can result in
some flux being carried into an infiltrated matrix powder. As a result of
incomplete separation of flux from the infiltrated drill bit, inclusions
can result within the final drill bit itself.

[0047] While many advantages of the present invention exist, only a few
are discussed herein. In some embodiments, the drill bit molds described
herein may comprise a filter that when used to form matrix drill bits can
remove at least a portion of the inclusions that may lead to defects in
the final matrix drill bits produced from the molds. Such inclusions can
detrimentally affect the mechanical properties of the final matrix drill
bits by, inter alia, acting as discontinuities in the metal matrix. The
term "inclusion" as used herein can refer to any impurities present in
the binder, the matrix powder, or any other components of the matrix
drill bit, and may include, but is not limited to, slag, dross, oxides,
silicates, and sulfides in the binder, oxides, silicates, and sulfides
formed during infiltration, and small fragments of the materials used to
form the mold. For example, the use of a flux may result in the formation
of inclusions that may typically float and solidify at the top of a mold
where it can be removed from the final product. However, incomplete
separation of flux from a matrix drill bit can result in inclusions
within the final drill bit itself. In some embodiments, the use of a mold
comprising a filter may allow for the reduction or elimination of the
flux from the matrix drill bit infiltration process, and consequently,
the reduction or prevention of any impurities entering the matrix drill
bit.

[0048] In some embodiments of the present invention, a drill bit mold
assembly may comprise a mold cavity having disposed therein an endpoint
of a flow path for molten binder material and at least one filter
disposed along the flow path before the endpoint of the flow path. As
used herein, the terms "mold cavity" or "cavity" refers to the space
within the drill bit mold assembly that defines the shape of the final
product. As used herein, the term "flow path" refers to a path that a
fluid may travel, e.g., a flow path for molten binder is the path the
binder may travel once molten during the production of a downhole tool,
e.g., a drill bit body. Said flow path generally has an endpoint where
the fluid, e.g., molten binder, comes to rest. It should be noted that
the terms "drill bit mold assembly" and "matrix drill bit mold" may be
used interchangeably herein.

[0049] In an embodiment of the present invention, a matrix drill bit mold
according to the present invention comprises a mold having a bottom and
at least one side; a core centrally disposed within the mold; and a
filter disposed above the bottom of the mold and within a space formed
between the at least one side of the mold and the core. The terms "matrix
drill bit" and "matrix drill bits" may be used in this application to
refer to "rotary drag bits," "drag bits," "fixed cutter drill bits" or
any other drill bit incorporating teaching of the present disclosure.
Such matrix drill bits may be used to form well bores or boreholes in
subterranean formations. The matrix drill bit mold may optionally
comprise additional components as necessary to facilitate the formation
of matrix drill bits of various shapes.

[0050] In some embodiments of the present invention, a drill bit mold
assembly may be formed by one or more piece. Examples of suitable pieces
and/or components of a drill bit mold assembly may include, but not be
limited to, a bottom, walls, sides, ledges, cores, metal blanks, legs,
mold inserts, binder bowls, funnels, gauge rings, or any combination
thereof. One skilled in the art should understand the operably
connectivity of said pieces, the configurations to place pieces in the
drill bit mold assembly, and the configurations where said pieces form
the drill bit mold assembly. In addition, a drill bit mold assembly may
be optionally assembled from various components to more easily form
complex matrix drill bit shapes by creating a more complex mold cavity.
In some embodiments, a mold cavity may be formed by two or more pieces
being operably connected. In some embodiments, a mold cavity may be
formed by the inner wall of a drill bit mold assembly and an outer wall
of a piece disposed in the drill bit mold assembly.

[0051] A wide variety of molds may be satisfactorily used to form matrix
drill bits in accordance with the teachings of the present disclosure.
Mold assembly 100 as shown in FIGS. 1-13 represents only examples of mold
assemblies satisfactory for use in forming a matrix drill bit body
incorporating teachings of the present disclosure. U.S. Pat. No.
5,373,907 entitled "Method And Apparatus For Manufacturing And Inspecting
The Quality Of A Matrix Body Drill Bit" which is incorporated herein in
its entirety, shows additional details concerning mold assemblies and
conventional matrix bit bodies.

[0052] In an embodiment, mold assembly 100 may have a bottom and at least
one side; a core centrally disposed within the mold; and a filter
disposed above the bottom of the mold and within a space formed between
the at least one side of the mold and the core. In an embodiment, mold
assembly 100 may comprise a single component (not shown). In such
embodiments, at least a portion of the mold may be broken upon completion
of the infiltration process to remove the drill bit. In some embodiments,
mold assembly 100 may include several components such as mold base 102,
gauge ring or connector ring 110 and funnel 120. Mold base 102, gauge
ring 110 and funnel 120 may be formed from graphite, consolidated sand,
or other suitable materials. Various techniques may be used including,
but not limited to, machining a graphite blank to produce mold base 102
with cavity 104 having a negative profile or a reverse profile of desired
exterior features for a resulting fixed cutter drill bit. For example
cavity 104 may have a negative profile which corresponds with the
exterior profile or configuration of blades 52 (illustrated in FIG. 14)
and junk slots or fluid flow passageways formed therebetween. The
formation of mold assembly 100 in several components may allow for the
reuse of at least one of the components to form multiple drill bits. For
example, funnel 120 may be removed after the infiltration process and
reused in a subsequent infiltration process.

[0053] In some embodiments as shown in FIG. 1, binder bowl 121 may be
disposed on top of mold assembly 100. In general, binder bowl 121 may be
used to hold the binder material, and optionally any flux, during the
infiltration process. When used in the infiltration process, the binder
material may melt to form a molten binder material that may flow through
the binder bowl 121 into the matrix powder disposed in the mold below.
Binder bowl 121 may be formed of a material similar to that used to form
the mold assembly 100, for example using graphite, consolidated sand, or
the like. Binder bowl 121 may be shaped so that it is disposed within the
upper portion of mold assembly 100. For example, binder bowl 121 may be
disposed on top of funnel 120. Binder bowl 121 may comprise one or more
openings formed in the bottom of the binder bowl 121 of an appropriate
size and shape so that any molten binder material within the binder bowl
can flow through openings 124 into mold assembly 100 below. Openings 124
may be of any size or shape so long as binder bowl 121 maintains
structural integrity when a binder material is placed on top of or within
the binder bowl 121 and used in an infiltration process. In some
embodiments as shown in FIGS. 9A-9C, openings 124 may be disposed in a
ring about the outer edge of binder bowl 121 such that any molten binder
material passing through openings 124 may pass between metal blank 36 and
the inner surface of mold assembly 100 and/or between metal blank 36 and
the outer wall of core 150. In some embodiments, a filter may be
integrated within the body of binder bowl 121 or otherwise support a
filter for filtering the binder material, as described in more detail
below.

[0054] As shown in FIG. 2, a plurality of mold inserts 106 may be placed
within cavity 104 to form respective pockets 58 in the blades 52 (blades
52 illustrated in FIG. 14). The location of mold inserts 106 in cavity
104 corresponds with desired locations for installing cutting elements 60
in associated blades 52. Mold inserts 106 may be formed from various
types of material such as, but not limited to, consolidated sand and
graphite. Various techniques such as brazing may be satisfactorily used
to install cutting elements 60 in respective pockets 58 upon removal of
the completed matrix drill bit from the mold.

[0055] Various types of temporary displacement materials may be
satisfactorily installed within cavity 104, depending upon the desired
configuration of a resulting matrix drill bit. Additional mold inserts
(not expressly shown) formed from various materials such as consolidated
sand and/or graphite may be disposed within cavity 104. Various resins
may be satisfactorily used to form consolidated sand. Such mold inserts
may have configurations corresponding with desired exterior features of
matrix drill bit body 50 (illustrated in FIG. 14) such as fluid flow
passageways formed between adjacent blades 52.

[0056] As shown in FIG. 1, before infiltration, displacement materials
such as consolidated sand may be installed within mold assembly 100 at
desired locations. Such displacement materials are shown at core 150 and
legs 142 and 144 extending therefrom. Once the metal solidifies after
infiltration, the displacement materials can be removed, leaving voids in
the resulting drill bit where the displacement materials were formerly
located. Such displacement materials may have various configurations. The
orientation and configuration of legs 142 and 144 may be selected to
correspond with desired locations and configurations of associated fluid
flow passageways or voids to respective nozzle outlets 54 (illustrated in
FIG. 14). The fluid flow passageways may receive threaded receptacles
(not expressly shown) for holding respective nozzles therein.

[0057] A relatively large, generally cylindrically shaped core 150, which
may be made from consolidated sand, may be placed on legs 142 and 144.
Core 150 and legs 142 and 144 may be sometimes described as having the
shape of a "crow's foot." Core 150 may also be referred to as a "stalk."
The number of legs extending from core 150 will depend upon the desired
number of nozzle openings in a resulting composite bit body. Legs 142 and
144 and core 150 may also be formed from graphite, consolidated sand, or
other suitable material.

[0058] A generally hollow, cylindrical metal blank 36 may be placed within
mold assembly 100. Metal blank 36 preferably includes inside diameter 37
which is larger than the outside diameter of core 150. Various fixtures
(not expressly shown) may be used to position metal blank 36 within mold
assembly 100. After desired displacement materials, including core 150
and legs 142 and 144, have been installed within mold assembly 100, a
matrix powder 132 as described in more detail below, may be placed within
mold assembly 100.

[0059] In an embodiment, a filter may be used to remove at least a portion
of any inclusions to produce a final matrix drill bit with fewer
inclusions and/or reduce the amount of flux required during the
infiltration process. Without intending to be limited by theory, filters
used in an infiltration process may function through a variety of
mechanisms. The primary mechanisms may include sieving, cake filtration,
and depth filtration. Sieving refers to the blocking of particles larger
than the filter's openings at or near the inlet of the flow. Cake
filtration refers to the build-up of inclusions on the filter's face,
which further aids filtering of inclusions during subsequent molten metal
flow. In an embodiment, cake filtration can be used to remove particles
larger than about 30 microns.

[0060] Depth filtration refers to the filtering mode in which inclusions
are physically attracted or bonded to the surface of the filter itself,
for example through a physically attractive force including, but not
limited to, gravity, friction, physical entrapment, chemically attractive
forces, Van der Waals forces, electrostatic attractive forces, or any
other similar force. In an embodiment, depth filtration is capable of
removing particles equal to or smaller than about 30 microns. Depth
filtration may be present with filters providing tortuous flow paths for
molten metal. The tortuousity provides an increasing probability for
particle capture as the inclusions within the molten metal contact the
filter surface due to transport phenomena such as inertia, sedimentation,
particle interception, and diffusion and then attach to the filter
surface through one of the attractive forces described above.

[0061] In some embodiments of the present invention, at least one filter
may be disposed along a flow path. In some embodiments of the present
invention, at least one filter may be disposed along a flow path and in
contact with the drill bit mold assembly, a piece thereof, a piece
disposed therein, or any combination thereof. In some embodiments of the
present invention, at least one filter may be disposed along a flow path
and an integral part of the drill bit mold assembly, a piece thereof, a
piece disposed therein, or any combination thereof. In some embodiments,
filters may be removable from the drill bit mold assembly, a piece
thereof, a piece disposed therein, or any combination thereof.

[0062] Filters suitable for use in the present invention can include any
filters capable of removing inclusions within the binder material during
the infiltration of matrix drill bits, and that are capable of
withstanding the infiltration conditions necessary to form a matrix drill
bit, which can include, for example, temperature and exposure to molten
binder material. Several filter types exist for use in the infiltration
process including, but not limited to, strainer filters, cellular
filters, screen filters, ceramic cloth filters, bed filters, bonded
particle filters, ceramic foam filters, or any other suitable filters.
Strainer filters can comprise a regular pattern of round openings or
elongated slits to form a straining surface that may trap inclusions
mainly through sieve filtration and cake filtration mechanisms, though
some bed filtration can occur. Similarly, cellular filters comprise a
regular structured array of various shapes that provide openings for
molten metal flow. The regular pattern of the cellular filters may have
an increased flow rate, reduced turbulence of the molten metal through
the filter, and reduced filter erosion as compared to strainer filters.
Screen filters may comprise one or more mesh screens with an optional
mesh, felt, or cloth disposed in front of and/or between the mesh
screens. Screen filters may provide moderate filtration, particularly of
larger particles and inclusions exceeding about 100 microns in diameter.
Ceramic cloth filters can comprise any type of fibrous material formed
from a ceramic or mineral material. Suitable ceramic cloths are
commercially available and can be obtained, for example, as INSWOOL®,
available from A.P. Green Industries, Inc. of Pennsylvania. Bed filters
generally refer to a loose bed of particulate filter material through
which a molten metal flows. Bed filters generally filter molten metal
through a bed filtration mechanism and may provide a high efficiency of
fine particulate filtration. Bonded particle filters generally comprise
particles (e.g., refractory grain such as Al2O3, SiC, etc.)
bonded together to form a rigid filter structure. Bonded particle filters
may have a porosity ranging from about 25% to about 50%. Ceramic foam
filters are produced by slurry coating a reticulated polyurethane
cellular foam, followed by drying and firing to burn out the precursor
foam. Ceramic foam filters may have a range of porosities, for example
from about 50% to about 85% porous, and can include a pore size
distribution suitable to capture a range of inclusion sizes. Suitable
filters are commercially available from various companies such as ASHLAND
INC. of Dublin, Ohio, and FOSECO METALLURGIC INC. of Cleveland, Ohio.
Dual-structure or multilayered ceramic foam filters may also be employed
to provide a desired level of filter efficiency. In some embodiments,
multilayered filters comprising several filter types may be used to
provide the desired filter efficiency.

[0063] In an embodiment, the choice of the filter type may be determined
at least in part by the desired efficiency of the filter. As used herein,
the term "filter efficiency" refers to the total weight of inclusions
removed from the molten metal stream through one or more filters based on
the inlet and outlet mass of the inclusions and expressed as a percentage
of the inlet inclusion mass (i.e., the difference between the inlet mass
of inclusions minus the outlet mass of inclusions, divided by the inlet
mass of inclusions). The filter efficiency may depend on a variety of
factors including, but not limited to, the nature of the molten metal
itself (e.g., binder composition, viscosity based on temperature, etc.),
the nature of the inclusions (e.g., size, shape, distribution), the
molten metal flow rate (e.g., which may depend on the total molten metal
head), the filter geometry (e.g., length, depth, total surface area), and
the balance between the amount of sieving, cake filtration, and depth
filtration. Without intending to be limited by theory, it is generally
believed that lower molten metal flow rates generally result in greater
filtration efficiency due to an increased probability that a given
inclusion will be trapped within the filter through depth filtration.
Similarly, a greater filter surface area can increase the probability of
capturing an inclusion. In addition to filter efficiency, consideration
of the filter design can take into account the mechanical properties of
the filter. For example, the filter may need to be thicker than necessary
for a desired efficiency in order to be able to mechanically support a
desired amount of binder material during the infiltration process.

[0064] Consideration may be given to the permeability, porosity and/or
pore size of the filter which can affect the pressure drop as molten
binder material passes through the filter. As a general trend, the
pressure drop through a filter increases with decreasing pore size and/or
decreasing porosity. In general, a greater pressure drop can require more
of a molten metal head that can result in more material being left above
the filter and a corresponding loss of material during the infiltration
process. In an embodiment, the permeability, pore size and/or porosity of
the filter can be chosen to control the rate of infiltration of the
molten binder material. Such an embodiment may be used to produce a
desired molten binder flow rate into the matrix powder during the
infiltration process. In an embodiment, the filter could be used to
reduce the turbulence of molten binder falling from the binder bowl
before it enters the matrix powder.

[0065] In an embodiment, a filter may be constructed of any material
capable of withstanding the infiltration process conditions while
maintaining the desired filtering efficiency. Suitable materials may
include, but are not limited to, ceramics such as alumina, zirconia,
cordierite, silica, mullite, silicon carbide, fiberglass, graphite, and
any combinations thereof. Additional suitable materials may include, but
are not limited to, suitable high temperature metals such as high
temperature steel, cobalt, tungsten, and molybdenum, any alloys thereof,
and any combinations thereof. One of ordinary skill in the art will
recognize that some metals and/or ceramics may be unsuitable for use in
the filters disclosed herein due to detrimental interactions with one or
more binder materials used to infiltrate the matrix powder. One of
ordinary skill in the art would be capable, with the benefit of this
disclosure, of choosing an appropriate filter material and filter design
for use with the matrix drill bit molds disclosed herein.

[0066] In an embodiment, a filter may be contacted with a flux prior to
use in an infiltration process. Suitable flux materials may adsorb or
absorb into a filter material during contact. As a result, the flux may
be capable of binding with some inclusions (e.g., metal oxides) during
the infiltration process while being contained in the filter material.
Without intending to be limited by theory, such an embodiment may help
remove some inclusions while preventing the free flow of flux that may
contaminate the final matrix drill bit. In an embodiment, the flux may be
contacted with the filter material using any technique known to one of
ordinary skill in the art. One suitable process may include doping the
filter material with an appropriate solution of a flux in a solvent
followed by solvent extraction (e.g., drying if the solvent is an aqueous
solution). Another suitable process may include contacting the filter
material with a flux material and heating the filter material so that the
flux melts and is allowed to adsorb or absorb into the filter material.
Any excess flux may be separated from the filter material prior to
cooling the filter material for use in the processes of the present
invention. Yet another suitable process may include contacting the filter
material with a flux carrying slurry and evaporating or heating the
slurry to allow the flux to coat the filter.

[0067] In an embodiment, a filter may be incorporated into the matrix
drill bit mold using any design in which the molten binder material
passes through at least a portion of the filter prior to contacting and
infiltrating the matrix powder. In general, the filter may be disposed
within the mold in one or more flow paths of the molten binder material.
In some embodiments, the filter may be disposed in and/or integrated with
a binder bowl. In some embodiments, the filter may be disposed in a flow
path of a molten binder material supplied from an external source. As
used herein, the term "external source" refers to any source of a molten
binder material other than a binder material placed in a binder bowl
and/or within the mold itself and heated to form a molten binder
material. Suitable examples of a molten binder material supplied from an
external source are discussed in more detail below.

[0068] In some embodiments, the filter may be disposed within a flow path
of a molten binder material within the mold. In an embodiment shown in
FIG. 3, filter 133 may be disposed about the core 150 and rest on the
metal blank 36. In this embodiment, the metal blank 36 supports filter
133 during the infiltration process, as described in more detail below.
Filter 133 may be designed to contact funnel 120 and core 150 so that the
molten binder material does not channel between filter 133 and funnel
120, or between filter 133 and core 150 during the infiltration process.
Filter 133 may comprise any of the filter types or combination of filter
types described herein that are capable of being supported on metal blank
36. For example, a bonded particle filter and/or ceramic foam filter may
be used along with an optional particulate material on top in this
embodiment.

[0069] In some embodiments, filter 133 may be disposed about core 150 and
supported on a ledge disposed in or integrated with mold assembly 100. As
shown in FIG. 4, ledge 165 can refer to any support structure disposed in
mold assembly 100 that is capable of supporting filter 133 within mold
assembly 100. In an embodiment, the ledge may be formed by the lower
portion of cutout 163 in funnel 120. In some embodiments, ledge 165 can
comprise a support structure disposed inside the funnel with or without
additional cutout 163. In some embodiments, funnel 120 can comprise a
horizontal ledge. In some embodiments, the ledge may be angled towards
the interior of mold assembly 100 so that upon placement of filter 133 in
mold assembly 100, a sealing engagement is achieved between the edge of
filter 133 and funnel 120. Such an embodiment may help prevent any
channeling of molten binder material between the edge of filter 133 and
the inner edge of funnel 120. Filter 133 may comprise any of the filter
types or combination of filter types described herein that are capable of
being supported on ledge 165. For example, a bonded particle filter
and/or ceramic foam filter may be used along with an optional particulate
material disposed on top.

[0070] In some embodiments as shown in FIG. 5, one or more filters may be
disposed within mold assembly 100 about metal blank 36. The filters 170,
172 may take the form of concentric rings disposed within mold assembly
100, though other shapes are possible if the mold assembly shape varies.
Metal blank 36 may have one or more ledges 167 disposed therein of a
suitable size and shape to support the one or more filters. In an
embodiment, filter 170 may be supported by ledge 167 in the outer
circumference of metal blank 36. Ledge 167 can comprise any support
structure suitable for holding filter 170 during the infiltration
process. In an embodiment, the lower portion of ledge 167 may have a
horizontal surface. In some embodiments, the lower portion of ledge 167
may have a surface disposed at an angle. In some embodiments, the ledge
may be angled so that filter 170 disposed between metal blank 36 and
funnel 120 has a sealing engagement with metal blank 36 and funnel 120 to
help prevent channeling of molten binder material between filter 170 and
metal blank 36 and/or funnel 120. In some embodiments, an additional
ledge and filter can be disposed between metal blank 36 and core 150.
Ledge 167 may be disposed on the interior circumference of metal blank 36
to support filter 172. Ledge 167 disposed between metal blank 36 and core
150 may be similar to or distinct from ledge 167 disposed between metal
blank 36 and funnel 120. In an embodiment, filter 172 can be used to
filter any molten binder material that passes between metal blank 36 and
core 150. Filters 170, 172 may comprise any of the filter types or
combination of filter types described herein that are capable of being
supported on ledge 167. For example, a bonded particle filter and/or
ceramic foam filter may be used along with an optional particulate
material disposed on top.

[0071] In an embodiment as shown in FIG. 6, a filter may be disposed
within and/or be integrated with core 150 within mold assembly 100. In
this embodiment, core 150 may have a hollow or carved out center suitable
for holding binder material 160 and/or receiving a molten binder material
during the infiltration process. Filter 133 may be disposed within the
lower portion of core 150 and may be sealingly engaged with the interior
of core 150. As a result, any molten binder material formed within the
core and/or flowing through the core can pass through filter 133 prior to
contacting and infiltrating matrix powder 132. In some embodiments,
filter 133 may be disposed in core 150, and a binder bowl (not shown) may
be used to funnel molten binder material into the center of core 150 such
that the molten binder material passes through filter 133 prior to
contacting and infiltrating matrix powder 132. Filter 133 may comprise
any of the filter types or combination of filter types described herein
that are capable of being disposed in or integrated with core 150.

[0072] In an embodiment as shown in FIG. 7, filter 174 may be disposed
within mold assembly 100. In some embodiments, the matrix powder 132 is
loaded in a mold such that the matrix powder may be subject to sloughing
or other movements during the infiltration process. For example, matrix
powder 132 may be loaded in mold assembly 100 such that the surface of
the matrix powder 132 is in a non-horizontal orientation within mold
assembly 100. In order to maintain a desired matrix powder form or shape
in mold assembly 100, filter 174 may be formed into a corresponding shape
and disposed in contact with matrix powder 132 to maintain its shape. In
some embodiments, filter 174 may be disposed below metal blank 36 and in
contact with funnel 120 such that matrix powder 132 is compressed and
held in place by filter 174. In an embodiment, filter 176 may be disposed
between metal blank 36 and core 150 to ensure that any molten binder that
passes between metal blank 36 and core 150 passes through a filter prior
to contacting and infiltrating matrix powder 132. Filters 174, 176 may
comprise any of the filter types or combination of filter types described
herein that are capable of being disposed within mold assembly 100. For
example, a bonded particle filter and/or ceramic foam filter may be used
along with an optional particulate material above or below the filter.

[0073] In some embodiments, the filter may be disposed in and/or
integrated with a binder bowl 121. As shown in FIG. 8, filter 133 may be
disposed within binder bowl 121. In an embodiment, filter 133 may
comprise a disc or any other suitably shaped filter material placed
within binder bowl 121 such that filter 133 contacts inner wall 180 of
binder bowl 121. In this embodiment, any molten binder material placed
within binder bowl 121 can pass through filter 133 prior to passing
through openings 124 in binder bowl 121. Filter 133 may comprise any of
the filter types or combination of filter types described herein that are
capable of being supported over openings 124 in binder bowl 121. For
example, a bonded particle filter and/or ceramic foam filter may be used
along with an optional particulate material disposed on top.

[0074] In another embodiment shown in FIGS. 9A, 9B, and 9C, filter 133 is
disposed within binder bowl 121 in either openings 124 or as an integral
part with binder bowl 121. In an embodiment, filter 133 is a separate
filter that is placed within openings 124 in binder bowl 121. Suitable
filter placement may be accomplished through the use of an interference
fit in which the filter 133 is pressed into the opening without
significantly damaging filter 133 or binder bowl 121. In another
embodiment, openings 124 in binder bowl 121 may comprise a tapered
profile in the vertical direction so that openings 124 are slightly
smaller at the bottom (i.e., the portion closer to the bottom of the
mold) than at the top. Filter 133 may comprise a corresponding tapered
profile so that the edge of filter 133 substantially contacts the edge of
opening 124 along its entire length. Alternatively, filter 133 may have a
non-tapered edge so that upon placement within tapered opening 124 of
binder bowl 121, contact is provided at the lower edge of filter 133 to
prevent channeling of the molten binder material around filter 133. In
still another embodiment, openings 124 in binder bowl 121 may comprise a
ledged profile such that at least a portion of the inner diameter of the
opening is smaller at the bottom than at the top, thus forming a ledge
upon which filter 133 may be placed. Filter 133 may have a corresponding
shape and diameter to that of the upper portion of opening 124 in binder
bowl 121. Upon placement of filter 133 in opening 124, the filter would
rest on the ledge at the bottom of the opening in binder bowl 121. An
exemplary top view of binder bowl 121 with filter 133 placed in openings
124 is shown in FIG. 9B.

[0075] In yet another embodiment, filter 133 may be incorporated into
binder bowl 121. In some embodiments, filter 133 may be incorporated into
binder bowl 121 during the manufacturing of the binder bowl 121 so that
the filter material may be integrally formed in the binder bowl material.
In an embodiment, filter 133 may be disposed within openings 124 of
binder bowl 121 during manufacturing such that the final binder bowl is
similar to a design in which filter 133 is disposed in openings 124 in
binder bowl 121. For example, filter 133 may be disposed in a graphite
binder bowl so that the graphite is formed around the edges of the filter
and securely holds the filter in place. In another embodiment, a
plurality of holes may be formed in binder bowl 121 to form a strainer
filter and/or cellular filter that forms the opening 124 of binder bowl
121. For example, the holes of a strainer filter may be directly formed
in a solid binder bowl blank. In an embodiment, filter 133 may be formed
in any suitable shape or pattern in binder bowl 121. For example, the
filter formed in the binder bowl from a binder bowl blank may be disposed
in a pattern around the circumference of the binder bowl, or the filter
can be formed as a pattern on the entire surface of the binder bowl. In
an embodiment as shown in FIG. 9C, filter 133 may form a continuous band
in binder bowl 121.

[0076] In still another embodiment shown in FIG. 10, filter 133 may
comprise a loose particulate material to form a bed filter. Filter 133
may be disposed on top of matrix powder 132 within mold assembly 100.
While FIG. 10 illustrates filter 133 comprising particulate material
disposed about metal blank 36 as well as core 150, more or less of the
particulate material may be used to selectively form a bed filter in
separate portions of the mold. For example, filter 133 may comprise
particulate material disposed only between metal blank 36 and the side of
funnel 120. In an alternative embodiment (not shown), a filter material
comprising a particulate material may be disposed above and supported by
a structured filter media (e.g., ceramic foam filter, bonded particle
filter, etc.). The structured filter media may in turn be supported by
metal blank 36 or some other structure within mold assembly 100. The
particulate material may have a particle size distribution that is
suitable to form a desired porosity and pore size distribution, which in
turn can affect the pressure drop through the particulate material bed
and filtration efficiency. In an embodiment, the particle size of the
particulate material may have a lower limit based on the particle size of
the matrix powder disposed in the matrix drill bit mold. Without
intending to be limited by theory, it is believed that the particle size
of the particulate material should be larger than the matrix powder
particle size to prevent the particulate material from being entrained in
the molten binder material and carried into the matrix powder during the
infiltration process.

[0077] In some embodiments, the filter may be disposed in a flow path of a
molten binder material supplied from an external source. In an embodiment
shown in FIG. 11, filter 133 may be disposed in the side of mold assembly
100 (e.g., in the side of funnel 120) such that a flow path for molten
binder material is provided between the mold assembly 100 and an outer
mold 190. The filter may comprise discrete filter elements disposed in
mold assembly 100, or the filter can comprise a ring of filter material
forming a portion of the side wall of mold assembly 100. In this
embodiment, mold assembly 100 may be disposed within the outer mold 190
that may provide the external source of molten binder material during the
infiltration process. Outer mold 190 may be of a sufficient diameter to
allow for binder material 160 to be placed between the inner wall of
outer mold 190 and the outer wall of mold assembly 100. Outer mold 190
may be constructed of a material similar to mold assembly 100. Filter 133
can filter any molten binder material passing from the outer mold 190
through filter 133 and into mold assembly 100 during the infiltration
process. Filter 133 may comprise any of the filter types or combination
of filter types described herein that are capable of being disposed in
and/or integrated with mold assembly 100, for example, in funnel 120.

[0078] In still another embodiment, the filter may be disposed in a flow
path of molten binder material supplied from an external source. As shown
in FIG. 12, filter 133 may be disposed in the side of mold assembly 100
(e.g., in the side of funnel 120) such that a flow path for molten binder
material is provided between the interior and the exterior of mold
assembly 100. External molten binder material source 192 may be in fluid
communication with the exterior surface of filter 133 disposed in mold
assembly 100. Suitable external molten binder material sources may
include, but are not limited to, separate containers within the same
furnace and/or external furnaces containing molten binder material. For
example, the external molten binder material source 192 may provide
molten binder material formed in a separate furnace and transported in a
ladle for transfer through filter 133 and into mold assembly 100. Filter
133 may comprise any of the filter types or combination of filter types
described herein that are capable of being disposed in and/or integrated
with mold assembly 100.

[0079] Mold assembly 100 may be used to form a matrix drill bit. In
general, a matrix drill bit comprises a matrix powder infiltrated with a
binder material in an infiltration process, as described in more detail
below. The matrix powder is placed within the mold assembly around any
mold inserts. The matrix powder generally lends desirable mechanical
properties to a matrix drill bit such as a high resistance to abrasion,
erosion and wear. The matrix powder can comprise particles of any erosion
resistant materials which can be bonded (e.g., mechanically) with a
binder to form a matrix drill bit. Suitable materials may include, but
are not limited to, carbides, nitrides, natural and/or synthetic
diamonds, and any combination thereof.

[0080] In an embodiment, a matrix powder may comprise tungsten carbide.
Various types of tungsten carbide may be used with the present invention,
including, but not limited to, stoichiometric tungsten carbide particles,
cemented tungsten carbide particles, and/or cast tungsten carbide
particles. The first type of tungsten carbide, stoichiometric tungsten
carbide, may include macrocrystalline tungsten carbide and/or carburized
tungsten carbide. The second type of tungsten carbide, cemented tungsten
carbide, may include sintered spherical tungsten carbide and/or crushed
cemented tungsten carbide. The third type of tungsten carbide, cast
tungsten carbide, may include spherical cast tungsten carbide and/or
crushed cast tungsten carbide. Additional materials useful as matrix
powder or as part of a matrix powder blend include, but are not limited
to, silicon nitride (Si3N4), silicon carbide (SiC), boron
carbide (B4C), cubic boron nitride (CBN), and any other materials
known to be useful as matrix powders.

[0081] The various materials useful as a matrix powder may be selected so
as to provide a matrix powder and final matrix drill bit that is tailored
for a particular application. For example, the type, shape, and/or size
of a particulate material used in the formation of a matrix drill bit may
affect the material properties of the matrix drill bit, including, for
example, fracture toughness, transverse rupture strength, and erosion
resistance. In an embodiment, the matrix powder may comprise a single
material or a blend of materials. In addition, two or more matrix powders
may be combined as necessary to form the matrix powder with the
characteristics described herein. In addition, two or more powders may be
separately loaded into a mold to form a matrix drill bit with properties
that can vary throughout the drill bit.

[0082] A binder material is used to infiltrate the matrix powder to form a
solid composite material. In an embodiment, the infiltrated matrix powder
may be formed during the infiltration process and can form a matrix drill
bit. The terms "binder" or "binder material" may be used in this
application to include copper, cobalt, nickel, iron, zinc, manganese,
tin, any alloys of these elements, any combinations thereof, or any other
material satisfactory for use in forming a matrix drill bit comprising a
matrix powder as described above. Such binders generally provide the
desired strength, ductility, toughness, and thermal conductivity for an
associated matrix drill bit.

[0083] In an embodiment, the drill bit mold comprising a filter according
to the present invention may be used to form at least a portion of a
matrix drill bit. Matrix drill bits can be used to drill oil and gas
wells, geothermal wells and water wells. As shown in FIG. 14, matrix
drill bits are often formed with a matrix drill bit body 50 having
cutting elements or inserts 60 disposed at select locations of exterior
portions of the matrix drill bit body, which may correspond to the mold
inserts 106 placed within cavity 104 (as shown in FIG. 2) to form pockets
58. Fluid flow passageways are typically formed in the matrix drill bit
body 50 to allow communication of drilling fluids from associated surface
drilling equipment through a drill string or drill pipe attached to the
matrix drill bit body 50.

[0084] FIG. 14 is a schematic drawing showing one example of a matrix
drill bit 20 that may be formed with a matrix drill bit mold in
accordance with teachings of the present disclosure. For embodiments such
as shown in FIG. 14, matrix drill bit 20 may include shank 30 with matrix
drill bit body 50 securely attached thereto. Shank 30 may be described as
having a generally hollow, cylindrical configuration defined in part by a
fluid flow passageway therethrough. Various types of threaded
connections, such as American Petroleum Institute (API) connection or
threaded pin 34, may be formed on shank 30 opposite from matrix drill bit
body 50.

[0085] In some embodiments, a generally cylindrical metal blank 36
(illustrated in FIGS. 1-13 may be attached to hollow, generally
cylindrical shank 30 using various techniques. For example, an annular
weld groove may be formed between adjacent portions of metal blank 36 and
shank 30. The fluid flow passageway or longitudinal bore preferably
extends through shank 30 and the blank. The blank and shank 30 may be
formed from various steel alloys or any other metal alloy associated with
manufacturing rotary drill bits.

[0086] A matrix drill bit may include a plurality of cutting elements,
inserts, cutter pockets, cutter blades, cutting structures, junk slots,
and/or fluid flow paths that may be formed on or attached to exterior
portions of an associated bit body after the matrix bit is removed from
the matrix drill bit mold. For an embodiment such as shown in FIG. 14, a
plurality of cutter blades 52 may form on the exterior of matrix drill
bit body 50. Cutter blades 52 may be spaced from each other on the
exterior of matrix drill bit body 50 to form fluid flow paths or junk
slots therebetween.

[0087] A plurality of nozzle outlets 54 may be formed in matrix drill bit
body 50. Respective nozzle 56 may be disposed in each nozzle outlet 54.
For some applications nozzle 56 may be described as an "interchangeable"
nozzle. Various types of drilling fluid may be pumped from surface
drilling equipment (not expressly shown) through a drill string (not
expressly shown) attached with threaded connection 34 and the fluid flow
passageways to exit from one or more nozzles. The cuttings, downhole
debris, formation fluids and/or drilling fluid may return to the well
surface through an annulus (not expressly shown) formed between exterior
portions of the drill string and interior of an associated well bore (not
expressly shown).

[0088] A plurality of pockets or recesses may be formed in blades 52 at
selected locations. Respective cutting elements 60 may be securely
mounted in each pocket to engage and remove adjacent portions of a
downhole formation. Cutting elements 60 may scrape and gouge formation
materials from the bottom and sides of a well bore during rotation of
matrix drill bit 20 by an attached drill string. In some embodiments,
various types of polycrystalline diamond compact (PDC) cutters may be
satisfactorily used as cutting elements 60. A matrix drill bit having
such PDC cutters may sometimes be referred to as a "PDC bit."

[0089] U.S. Pat. No. 6,296,069 entitled "Bladed Drill Bit with Centrally
Distributed Diamond Cutters" and U.S. Pat. No. 6,302,224 entitled
"Drag-Bit Drilling with Multi-Axial Tooth Inserts" show various examples
of blades and/or cutting elements which may be used with a composite
matrix bit body incorporating teachings of the present disclosure. It
will be readily apparent to persons having ordinary skill in the art that
a wide variety of fixed cutter drill bits, drag bits and other drill bits
may be satisfactorily formed with a matrix drill bit body incorporating
teachings of the present disclosure. The present disclosure is not
limited to matrix drill bit 20 or any specific features as shown in FIG.
14.

[0090] A matrix drill bit may be formed using the matrix drill bits of the
present invention that may have a functional gradient. In this
embodiment, one or more portions of the matrix drill bit (e.g., an outer
layer) may be formed using one type of matrix powder disclosed herein,
while a different matrix powder composition is used to form the remaining
portions of the matrix drill bit (e.g., the interior portions). As an
example, a resulting matrix drill bit can be described as having a
"functional gradient" since the outer portions may have improved erosion
resistance while the inner portions may exhibit improved mechanical
strength by having a different material composition. Methods of forming
matrix drill bits with different functional zones is described in U.S.
Pat. No. 7,398,840 entitled "Matrix Drill Bits and Method of
Manufacture."

[0091] A tool comprising a matrix drill bit in whole or in part as formed
in accordance with the teachings of the present invention may be used for
other applications in a wide variety of industries and is not limited to
downhole tools for the oil and gas industry.

[0092] The matrix drill bits of the present invention may be formed using
any technique known in the art. An embodiment of a typical infiltration
process may be described with reference to FIGS. 3 through 13. In an
embodiment, a infiltration process for producing matrix drill bits may
begin by forming mold assembly 100 in the shape of a desired component.
In some embodiments, the mold assembly 100 may be formed as a single
piece with interior features corresponding to the final matrix drill bit
features. In some embodiments, mold assembly 100 may comprise two or more
pieces. For an embodiment in which mold assembly 100 comprises a
plurality of pieces, mold assembly 100 may be formed by disposing gauge
ring 110 onto mold base 102, for example by threading gauge ring 110 onto
mold base 102. Funnel 120 may be disposed onto the top of gauge ring 110
to extend mold assembly 100 to a desired height to hold the matrix
materials and binder material as described above. For example, funnel 120
may be threaded onto gauge ring 110. Displacement materials such as, but
not limited to, mold inserts 106, legs 142 and 144 and core 150 may then
be loaded into mold assembly 100 if not previously placed in cavity 104.
Metal blank 36 may be loaded into mold assembly 100.

[0093] In an embodiment, a matrix powder may be loaded into mold assembly
100. As described above, a combination of matrix powders may be loaded
into mold assembly 100 or a plurality of matrix powders may be loaded
into mold assembly 100 in layers or in a graduated fashion to create the
desired properties within the finished matrix drill bit. As mold assembly
100 is being filled with matrix materials, a series of vibration cycles
may be induced in mold assembly 100 to assist packing of matrix powder
132. The vibrations may help to ensure a consistent density of the matrix
powder 132 within a desired range required to achieve desired
characteristics for matrix drill bit body 50.

[0094] In an embodiment, a filter may be disposed within mold assembly
100. The filter may be located in various locations depending on the
nature of the filter and the specific mold assembly 100 used to form the
matrix drill bit. In an embodiment shown in FIG. 3, filter 133 may be
disposed about core 150 and rest on metal blank 36. In this embodiment,
metal blank 36 may support filter 133 during the infiltration process. In
some embodiments as shown in FIGS. 4 through 7, one or more filters may
be disposed within mold assembly 100 and supported on a ledge in the side
of mold assembly 100, supported on a ledge on the metal blank 36, and/or
disposed about metal blank 36 and core 150. In some embodiments, the
filter may be disposed within or form a part of core 150. In an
embodiment, binder material 160 may be placed on top of the filter
material. In an embodiment in which the filter is a part of the core,
binder material 160 may be disposed within the core. In some embodiments,
binder material 160 may be covered with a flux layer (not expressly
shown). A cover or lid (not expressly shown) may then be placed over mold
assembly 100.

[0095] In another embodiment shown in FIG. 13, filter 133 may be disposed
about core 150 and rest on metal blank 36. In this embodiment, metal
blank 36 may support filter 133 during the infiltration process. In some
embodiments as shown in FIGS. 4 through 7, one or more filters may be
disposed within mold assembly 100 and supported on a ledge in the side of
mold assembly 100, supported on a ledge on metal blank 36, and/or
disposed about metal blank 36 and core 150. In some embodiments, the
filter may be disposed within or form a part of core 150. Binder material
160 may be placed on top of a binder bowl 121, and optionally may be
covered with a flux layer (not expressly shown). A cover or lid (not
expressly shown) may then be placed over mold assembly 100. During the
infiltration process, molten binder material may flow from the binder
bowl, through openings 124 in binder bowl 121, and through the filter
disposed within the mold assembly to infiltrate matrix powder 132. In an
embodiment in which the filter is a part of the core, a funnel or other
flow control device may be used to channel the molten binder material
from binder bowl 121 into the center of core 150.

[0096] In another embodiment shown in FIGS. 9A, 9B, and 9C, filter 133 is
disposed within binder bowl 121, within openings 124, and/or as an
integral part with binder bowl 121, as described in more detail above.
Binder material 160 may be placed on top of binder bowl 121. Binder
material 160 may be covered with a flux layer (not expressly shown). A
cover or lid (not expressly shown) may then be placed over mold assembly
100. During the infiltration process, molten binder material may flow
from binder bowl 121, through filter 133 disposed within openings 124 in
binder bowl 121 to infiltrate matrix powder 132.

[0097] In still another embodiment shown in FIG. 10, filter 133 may
comprise a loose particulate material to form a bed filter. The filter
133 may be disposed on top of the matrix powder within the mold. In an
alternative embodiment (not shown), a filter material comprising a
particulate material may be disposed above and supported by a structured
filter media (e.g., ceramic foam filter, bonded particle filter, etc.) as
one or more filter elements. The structured filter media may in turn be
supported by metal blank 36, a ledge in the mold assembly, a ledge in the
metal blank, or some other structure within mold assembly 100. Binder
material 160 may be placed directly on top of the filter or filters or
within a binder bowl. Binder material 160 may be covered with a flux
layer (not expressly shown). A cover or lid (not expressly shown) may
then be placed over mold assembly 100. During the infiltration process,
molten binder material may flow through filter 133 to infiltrate matrix
powder 132. If a binder bowl is used to hold the binder material during
the infiltration process, the molten binder material may flow from the
binder bowl 121, through filter 133 to infiltrate matrix powder 132.

[0098] In still another embodiment shown in FIG. 11, filter 133 may be
disposed in the side of mold assembly 100. The mold assembly may be
placed in an outer mold 190 and binder material 160 may be loaded into
the annular space created between outer mold 190 and mold assembly 100.
Binder material 160 may be covered with a flux layer (not expressly
shown). A cover or lid (not expressly shown) may then be placed over mold
assembly 100 and outer mold 190. During the infiltration process, molten
binder material may flow through filter 133, into the interior of mold
assembly 100 to infiltrate matrix powder 132.

[0099] In yet another embodiment shown in FIG. 12, filter 133 may be
disposed in the side of mold assembly 100. External molten binder
material source 192 may be in fluid communication with the exterior
surface of filter 133 disposed in mold assembly 100. During the
infiltration process, a binder material may be melted in the same or a
different furnace and transferred to the mold assembly to flow through
filter 133, and into the interior of mold assembly 100 to infiltrate
matrix powder 132.

[0100] Mold assembly 100 and materials disposed therein (or operably
connected thereto) may be preheated and then placed in a furnace (not
expressly shown). When the furnace temperature reaches the melting point
of binder material 160, molten binder material may infiltrate matrix
powder 132. The melting point of the binder may vary depending on the
binder material composition, and may generally be in the range of from
about 590° C. (1100° F.) to about 1230° C.
(2250° F.). A preferred range may be about 815° C.
(1500° F.) to about 1230° C. (2250° F.). Proper
infiltration and solidification of binder material 160 within matrix
powder 132 may be important at locations adjacent to features such as
nozzle outlets 54 and pockets 58. Improved quality control from enhanced
infiltration of binder material 160 into matrix powder 132 that forms
respective blades 52 may allow designing thinner blades 52. Mold assembly
100 may then be removed from the furnace and cooled at a controlled rate.
Upper portions of mold assembly 100 such as funnel 120 may have increased
insulation (not expressly shown) as compared with mold base 102. As a
result, hot, liquid binder material in lower portions of mold assembly
100 will generally start to solidify before hot, liquid binder material
in the upper portions of mold assembly 100 solidifies.

[0101] It should be noted that cooling may be active (e.g., passing a gas
over and/or around the mold assembly or placing the mold assembly in a
cooled environment) or passive (e.g., allowing the mold assembly to cool
in ambient conditions).

[0102] Once cooled, mold assembly 100 may be broken away to expose
composite matrix drill bit body 50 as shown in FIG. 14. In some
embodiments in which mold assembly 100 comprises a plurality of pieces,
some portions of mold assembly 100 may be removed in a manner that allows
the reuse of that portion. For example, funnel 120 may be removed and
reused in a subsequent infiltration process. Subsequent processing
according to well-known techniques may be used to produce matrix drill
bit 20. In some embodiments, matrix drill bit 20 may be processed to
remove any filter material remaining in the drill bit. For example, if
the filter is disposed above metal blank 36 or about metal blank 36, the
filter material and any remaining binder material may be removed prior to
finishing matrix drill bit 20. As another example, cutting teeth may be
disposed in the cutter pockets by brazing after the matrix drill bit is
removed from mold assembly 100.

[0103] In an embodiment, a method comprises providing a matrix drill bit
formed using a matrix drill bit mold comprising a filter according to the
present disclosure. The matrix drill bit generally comprises a binder,
and a matrix powder. The drill bit also has at least one cutting element
for engaging a formation. The drill bit is then used to drill a well bore
in a subterranean formation.

[0104] In some embodiments of the present invention, a drill bit mold
assembly may include a mold cavity having disposed therein an endpoint of
a flow path for molten binder material and at least one filter disposed
along the flow path before the endpoint of the flow path.

[0105] In some embodiments of the present invention, a drill bit mold
assembly may include a mold cavity having disposed therein an endpoint of
a flow path for molten binder material; at least a portion of at least
one piece disposed in the mold cavity; at least one filter disposed along
the flow path before the endpoint of the flow path; and a binder bowl
operably attached to the mold cavity and disposed along the flow path at
or before at least one filter.

[0106] In some embodiments of the present invention, a drill bit mold
assembly may include a mold cavity having disposed therein an endpoint of
a flow path for molten binder material and at least one filter disposed
along the flow path before the endpoint of the flow path. The mold cavity
may be formed by at least one inner wall of the drill bit mold assembly
and an outer wall of a piece disposed in the drill bit mold assembly.

[0107] Some embodiments of the present invention may involve placing a
matrix powder within the mold cavity; placing a binder material along the
flow path before the filter; melting at least a portion of the binder
material to form the molten binder material; passing the molten binder
material through the filter so as to infiltrate the matrix powder; and
cooling (actively or passively) the binder material to form a drill bit.
Generally a drill bit mold assembly may include a mold cavity having
disposed therein an endpoint of a flow path for a molten binder material
and at least one filter disposed along the flow path before the endpoint
of the flow path.

[0108] To facilitate a better understanding of the present invention, the
following examples of preferred embodiments are given. In no way should
the following examples be read to limit, or to define, the scope of the
invention.

EXAMPLES

Example 1

[0109] Two test pins were produced using SEDEX® filters (ceramic foam
filters, available from Foseco) to reduce the inclusions in the resultant
pins. A pin mold was produced with a three-tier cavity, shown in FIGS.
15A-D in a cross-sectional view, a top view, a picture without the
filter, and a picture with the filter, respectively. The three-tier
cavity having a closed bottom and open top has, from bottom to top, a
first cylinder having a 1.91 cm (0.75'') diameter and a 8.26 cm (3.25'')
height, a cube having a 2.54 cm (1.00'') height and 3.81 cm (1.50'')
square cross-section, and a second cylinder having a 7.62 cm (3.00'')
diameter and a 2.54 cm (1.00'') height. Overall the pin mold has an outer
diameter of 8.89 cm (3.50'') and height of 13.97 cm (5.50'').

[0110] The matrix material of D63 (tungsten carbide powder, available from
HC Stark) was loaded into the first cylinder and vibrated to settle the
powder. The final tungsten carbide powder level was 5.1 cm (2'') in
height. Then 0.64 cm (1/4'') of M70 (tungsten powder, available from HC
Stark) was loaded above the tungsten carbide and vibrated to settle. A
SEDEX® filter cut to (0.8'') thick by (1.5'') square was placed in the
second tier (square tier) of the three-tier mold cavity. Clay was placed
around the outer edges of the filter to hold the filter in place. In the
first mold cavity, approximately 300 g of binder was added on top of the
filter. In the second mold cavity, approximately 300 g of binder and 6
grams of Harris 600 flux (borax and boric acid, available from Harris
Products) was added on top of the filter. A graphite lid with two 9/64''
diameter atmosphere exposure holes was then placed on top of the mold.

[0111] The molds were placed in a lab furnace preheated to 1150° C.
(2100° F.) and held for approximately 1 hour. No atmosphere
control was used inside the furnace. Then the molds were removed from the
furnace and allowed to cool under ambient conditions. Once cool, the pins
were removed from the pin molds.

[0112] Both pins were successfully infiltrated, final pins shown in FIG.
16A (side view of the resultant pins) and 16B (top view of the second pin
showing the filter covered with trapped inclusion material). The filter
of the second pin (sample including flux) floated out of the second,
square tier during infiltration. However, the filter demonstrated
effective trapping of oxides as evidenced by the filter having a reddish
material (oxides) trapped in and on the filter.

[0113] Scanning electron microscopy (SEM) and electro dispersive
spectroscopy (EDS) were performed on portions of the filters after
infiltration. Table 1 below provides the EDS data corresponding to the
locations analyzed on the sample (labeled as "spots" overlaying the SEM
images). Spot #1 corresponds to FIG. 17, which is an SEM micrograph of
the filter without any treatment. Spots #2-#3, #4-#5, and #6-#7
correspond to FIGS. 18, 19, and 20, respectively, which are SEM
micrographs of different areas of the filter after production of the
first pin not using flux. Spots #8-#10, #11-#12, and #13-#14 correspond
to FIGS. 21, 22, and 23, respectively, which are SEM micrographs of
different areas of the filter after production of the second pin using
flux. It should be noted that the samples were not sputter coated before
SEM and EDS analysis.

[0114] The SEM images demonstrate that the filters have trapped material
on the surface and in the pores of the filter, shown in FIGS. 18-23 as
compared to FIG. 17 (a new filter). The EDS results show the filter
having trapped manganese sulfides and magnesium oxides. In pin 2, flux
was also trapped by the filters, evident by the increased sodium levels.
(It should be noted that boron is not detectable by normal EDS
equipment.) Manganese sulfides, magnesium oxides, and flux are primary
sources of inclusions. Silicon oxides are another common inclusion but
cannot be discerned in these samples from the silicon in the filter
material.

[0115] Therefore, the present invention is well adapted to attain the ends
and advantages mentioned as well as those that are inherent therein. The
particular embodiments disclosed above are illustrative only, as the
present invention may be modified and practiced in different but
equivalent manners apparent to those skilled in the art having the
benefit of the teachings herein. Furthermore, no limitations are intended
to the details of construction or design herein shown, other than as
described in the claims below. It is therefore evident that the
particular illustrative embodiments disclosed above may be altered,
combined, or modified and all such variations are considered within the
scope and spirit of the present invention. The invention illustratively
disclosed herein suitably may be practiced in the absence of any element
that is not specifically disclosed herein and/or any optional element
disclosed herein. While compositions and methods are described in terms
of "comprising," "containing," or "including" various components or
steps, the compositions and methods can also "consist essentially of" or
"consist of" the various components and steps. All numbers and ranges
disclosed above may vary by some amount. Whenever a numerical range with
a lower limit and an upper limit is disclosed, any number and any
included range falling within the range is specifically disclosed. In
particular, every range of values (of the form, "from about a to about
b," or, equivalently, "from approximately a to b," or, equivalently,
"from approximately a-b") disclosed herein is to be understood to set
forth every number and range encompassed within the broader range of
values. Also, the terms in the claims have their plain, ordinary meaning
unless otherwise explicitly and clearly defined by the patentee.
Moreover, the indefinite articles "a" or "an," as used in the claims, are
defined herein to mean one or more than one of the element that it
introduces. If there is any conflict in the usages of a word or term in
this specification and one or more patent or other documents that may be
incorporated herein by reference, the definitions that are consistent
with this specification should be adopted.